The novel takes place at the turn of the 20th century, at the end of the colonial period and beginning of the modern era. Britain colonizes Nigeria in an effort to keep up with the rest of the European colonial powers who are dividing up Africa for its natural resources. Although the slave trade had been banned, the Ibo culture is threatened by extinction because of the institutional (churches, legal system) and technological (weapons, infrastructure) advancements of the Empire.

Setting is also important before the colonists appear. In the village itself, the important settings are as follow:

Okonkwo's compound: with its many huts, yam farm

the Oracle of the Hills and Caves

the Umuofian village in relation to the neighboring villages (Mbaino, etc...)

the Evil Forest

Mbanta (Okonkwo's exiled Motherland)

All of these places "fall apart" as a result of the colonization. The center of the village, Okonkwo's compound, becomes a place of suicide, a portent that signals the end of his people's culture. According to his friend Obierka, Okonkwo was the greatest of men; therefore, his exile, death, a destruction of property forms the void for the entire death of Umuofia.

In this novel, the setting is the most important element of fiction, I think, because it is the foundation of the plot, them and characters. it takes place in the village called Umuofia in Nigeria, and the time frame is around 1800. This section of Africa is just starting to be colonized by the British and the eventual colonization of the Ibo people leads to things "falling apart" for the main character, Okonkwo. Okonkwo's stubbornness and pride add to his downfall, but he is also a traditional male Ibo who either was incapable or unwilling to change and adapt and because of this, his life falls apart and he eventually commits suicide.

There is a good analysis of this novel here on enotes and I will not repeat what is already there, but you can see that this is a novel that could not be set just anywhere at any time - its setting is crucial to the other elements of the novel and the setting is particularly important to the theme and characterization.